This invention relates to systems and methods for control of fuel delivery to vehicle engines and, in particular, to a system and method for determining the mass of charged air in a cylinder of the engine.
A conventional vehicle having a fuel-injected internal combustion engine includes a system for controlling the amount of fuel injected into each cylinder of the engine during a combustion event. The amount of fuel is controlled to achieve an optimal air-fuel ratio in the cylinders and thereby reduce emissions of hydrocarbons (HC), carbon monoxide (CO) and nitrous oxides (NOx). In order to the determine the proper amount of fuel to be injected into the cylinder, the system determines or estimates the mass of charged air introduced to the cylinder. One conventional system for determining the mass of charged air is known as the xe2x80x9cspeed-densityxe2x80x9d system. The speed-density system relies on measurements or estimates of engine speed, intake manifold pressure, and charge temperature. Conventional vehicles, however, also frequently include a system for recirculating exhaust gas into the engine cylinders (also for the purpose of reducing emissions and improving fuel efficiencies). The variable amount of exhaust gas effects the intake of the charged air mass and the pressure in the intake manifold. Accordingly, the speed-density system often provides inaccurate measurements of the charged air mass in vehicles with an exhaust gas recirculation system.
U.S. Pat. No. 5,205,260 discloses a system for determining the charged air mass in an engine cylinder and attempts to account for recirculated exhaust gas through the estimation of partial pressures for the recirculated exhaust gas and the charged air in the intake manifold. The system, however, requires complex calculations and therefore requires a relatively large amount of resources from the vehicle""s electronic control unit. Further, the system is still subject to significant errors in determining the charged air mass in the presence of recirculated exhaust gas.
There is thus a need for a system and method for determining the mass of charged air in a cylinder of an internal combustion engine that will minimize and/or eliminate one or more of the above-identified deficiencies.
The present invention provides a system and a method for determining the mass of charged air in a cylinder of an internal combustion engine having an intake manifold communicating with an engine cylinder. A method in accordance with the present invention includes the step of determining a temperature of a combination of charged air and recirculated exhaust gas inducted into the engine cylinder. The method also includes the step of determining a total mass flow rate responsive to a pressure in the intake manifold and the temperature of the combination of charged air and recirculated exhaust gas. The total mass flow rate includes a mass flow rate of the charged air and a mass flow rate of the recirculated exhaust gas. The total mass flow rate may also include other components such as purge flow from a charcoal canister. The method further includes the step of calculating the mass of charged air from the total mass flow rate.
A system in accordance with the present invention includes an electronic control unit that is configured, or encoded, to perform several functions. In particular, the unit is configured to determine a temperature of a combination of charged air and recirculated exhaust gas inducted into the engine cylinder. The system is also configured to determine a total mass flow rate responsive to a pressure in the intake manifold and the temperature of the combination of charged air and recirculated exhaust gas. The total mass flow rate again includes a mass flow rate of the charged air and a mass flow rate of the recirculated exhaust gas. The system is further configured to calculate the mass of charged air from the total mass flow rate.
The present invention represents an improvement as compared to conventional systems and methods for determining the mass of charged air in engine cylinders. In particular, the inventive system and method accurately account for recirculated exhaust gas in the engine cylinders in determining the charged air mass. Further, the inventive system and method accomplish this task using an algorithm and calculations that are less complex than conventional systems and methods. As a result, the inventive system and method do not require as many resources from the vehicle""s electronic control unit.
These and other advantages of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.